S W I TC H
Analysts
say some vendors are confusing buyers by abusing the term, applying it to
products that range from bridges to routers.
A LAN
switch - in its purest form - is a multiport Layer 2 device that forwards
packets at full wire speed. "A switch connects traffic based on a very
large-scale integration (VLSI) hardware process and uses essentially static
rules," said Thomas Nolle, president of CIMI Corp., a consultancy in
Voorhees, N.J. By contrast, a router steers traffic based on its address, using
dynamically adaptable rules.
The
switch label sprang up in the LAN industry as a way to differentiate hubs,
which create shared-media LANs, and another kind of device - such as Kalpana,
Inc.'s EtherSwitch - that connects traffic based on a static port-to-media
access control (MAC) address association, Nolle said.
Since the
introduction of the EtherSwitch in the late 1980's, the industry has understood
it - and devices like it - to be LAN switches.
But
building a network loaded with LAN switches can create broadcast storms, which
must be controlled with routing. And so the Layer 3 switch - and all the
confusion - emerged.
These new
"switches," like good ol' LAN switches, can make forwarding decisions
based on the packet's destination address. But they also have the intelligence
to make decisions based on Layer 3 information stored inside the packet. So
these "Layer 3 switches" really are not switches at all, but routers
with faster frame-forwarding capabilities.
"By
definition, there can be no such thing as a Layer 3 switch," said Kevin
Tolly, president of The Tolly Group, a consulting and testing firm in
Manasquan, N.J.
To further muddy the waters, LAN switches are different from circuit
switches - found in telephone networks - which send voice and data traffic
across a dedicated communication path between the sender and receiver. Those
are more closely akin to ATM switches, which work in basically the same way.
Confused?
You're not alone. "We're confusing the daylights out of everyone, and the
poor users are left scratching their heads," said Soni Jiandani, director
of marketing for LAN switching at Cisco Systems, Inc. "The lines across
the OSI layers are getting blurred, because everything is called a switch
now."
If some vendors are calling a multiport bridge a switch and others are
calling a router a switch, who is right?
"It
doesn't make a difference what you call the product. All that matters is
whether you are processing the packet at Layer 2 or Layer 3," Tolly said.
"If it's at Layer 2, it's a switch, and if it's at Layer 3, it's a
router."
Ah, but
it does matter what the device is called - from a marketing perspective.
"Layer
3 switching is really just a new buzzword for routing," said Patrick
Limpach, network services engineer at Case Western Reserve University in
Cleveland. But he pointed out that vendors may sell more gear if they go with
the switch nomenclature.
"If
you call it a switch, people will buy it," he said. But if you call it a
router, people might worry because their CEO may have read a white paper that
says routers are out and switches are in."
While
senior executives may get caught up in the marketing hype, Limpach said few
engineers are fooled.
"I
know what features I'm looking for, and I'm not just going to take any box with
a swizzy-bang name and buy it because it sounds good or it is painted pretty
colors," he said.
But more and more, the most important feature customers are looking for
in a LAN device is a combination of switching and routing. And that helps
explain the fuzzy definition associated with a switch.
"What
we're really seeing is the two types of products converging," Tolly said.
"The vendors who previously only sold switches - like Cabletron - are
adding basic Layer 3 capability. And the folks that only sold routers before -
like Cisco - are trying to make them as fast as switches."
And in so
doing, many vendors, such as Bay Networks, Inc., offer combination products
that are being labeled as routing switches. For example, Bay's Switch Node
device sounds like a switch, but is really a fast IP router.
"The
fact is, people just don't want to talk about pure routers anymore unless
referring to the WAN," Tolly said. "When it comes to the campus LAN,
switches, with a variety of different capabilities, will become the device name
of choice," he said.
In fact,
the reason some vendors are latching onto the switch term is to detach
themselves from the router's negative connotation.
"The
term router is getting the same type of negative association that front-end
processor (FEP) got near the end of its life," Tolly said. "In the
beginning, the FEP was this great device because it saved you all kinds of
money by off-loading work from your extremely expensive mainframe, just as the
router was an expensive, powerful box that brought you all kinds of
functionality. And now you can get as much functionality as you need from much
less expensive and faster boxes."
And in an
attempt to steer clear of routing's bruised reputation, vendors have confused
customers by labeling every little LAN device a switch.
But this
is not the first time the term "switch" has been confused in the
industry. Remember the muddled meaning of switches vs. port switches? Vendors
such as Bytex Corp. offered port switching hubs, which let customers group
certain ports on the same LAN segment. Then when "real" LAN switches
came on the scene from vendors such as Kalpana, customers were confused about
getting dedicated bandwidth on every port, industry observers said.
And
believe it or not, some of this confusion may be intentional. When there is
confusion in the industry, customers are often forced to cling to their
incumbent vendor for product direction, analysts said. So it may not be in the
best interest of the Big Four internetwork vendors to clarify the definition of
a switch.
The fact is, a true switch operates at - and only at - Layer 2. If the box offers Layer 3 capabilities, it just ain't a switch. It's a fast router.